arXiv subjects

Asoka Biswas

Publications and source records attributed to Asoka Biswas.

At least 19 recordsLinked to original sources

arXiv2026

Squeezing-Fueled Quantum Otto Engine via Measurement-Induced Cooling: The Two-Qubit Quantum Rabi Model

We investigate a quantum Otto engine (QOE) constructed from the two-qubit quantum Rabi model, operating within a cavity quantum electrodynamics (QED) architecture. The engine operates with two qubits as the working substance and a single non-Markovian hot thermal bath, modeled via the hierarchical equations of motion (HEOM) formalism. In place of a conventional cold thermal reservoir, the cooling stroke is realized through a projective measurement protocol on the cavity mode, which acts as an ancillary subsystem and effectively mimics a cold bath for the qubit working medium via measurement back-action. A squeezing drive applied to the cavity mode serves as a quantum fuel. We demonstrate that cavity squeezing systematically enhances both the power output and operational efficiency of the engine - the work extracted per unit of heat drawn from the hot bath-driving it above the standard quantum Otto limit. In the limit-cycle regime, the efficiency, while remaining above the Otto bound throughout, asymptotically converges to it from above. This identifies squeezing as a controllable quantum resource for thermodynamic optimization. Our results reveal that the interplay between qubit-cavity coupling, measurement-induced cooling, and non-equilibrium squeezing gives rise to a multi-resource thermodynamic architecture with performance characteristics inaccessible to conventional two-bath quantum Otto engines, thereby providing a concrete route toward experimentally realizable quantum heat engines in cavity QED platforms.

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arXiv2026

Multipartite synchronization residuals in driven-dissipative spin networks

We introduce a phase-space measure of quantum synchronization that quantifies relative phase localization for two-qubit and three-qubit systems. This measure is built from the first angular moments of phase distributions obtained from Husimi-Q quasiprobability functions. Using this framework, we formulate a new class of synchronization residuals, motivated by subadditivity-type hierarchies of information-theoretic measures. We investigate these residuals in a driven-dissipative quantum Rabi network in the dispersive adiabatic regime. We show that, for two qubits, collective synchronization remains bounded by single-qubit contributions yielding a non-negative bipartite residual. The three-qubit nonequilibrium steady state exhibits a negative tripartite residual, which indicates collective phase synchronization, which cannot be described by pairwise decomposition. The corresponding entropy-based residuals, however, remain non-negative in both cases. Our results therefore, underscore that phase-sensitive synchronization measures and entropic correlation measures probe distinct aspects of open-system dynamics.

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arXiv2026

Quantum synchronization between two strongly driven YIG spheres mediated via a microwave cavity

We present a theoretical study of synchronization between two strongly driven magnon modes indirectly coupled via a single-mode microwave cavity. Each magnon mode, hosted in separate Yttrium Iron Garnet spheres, interacts coherently with the cavity field, leading to cavity-mediated nonlinear coupling. We show, by using input-output formalism, that both classical and quantum synchronization emerge for appropriate choices of coupling, detuning, and driving. We find that thermal noise reduces quantum synchronization, highlighting the importance of low-temperature conditions. This study provides useful insights into tunable magnonic interactions in cavity systems, with possible applications in quantum information processing and hybrid quantum technologies.

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arXiv2025

Ancilla measurement-based Quantum Otto engine using double-pair spin architecture

We present a quantum heat engine model utilizing a dual spin-pair architecture, wherein an Otto-like cycle is implemented using a single heat bath. The conventional cold bath is replaced by a measurement protocol, enabling engine operation without the need for a second thermal reservoir. Unlike standard quantum heat engines, our framework employs an ancillary spin pair in a two-dimensional configuration to regulate performance. Operating in finite time, the engine attains finite power, which is enhanced through quantum correlations, specifically correlation between spin pairs and projective measurements on the ancillary pair. The system consists of dual qubit pairs, where one pair serves as the working medium and the other as an ancillary system facilitating measurement-induced heat exchange. We demonstrate that the engine efficiency can exceed the standard quantum Otto limit through local control of the ancillary pair while maintaining nonzero power output. Moreover, correlation between spin pairs enables efficiency modulation via the measurement basis, underscoring the role of quantum resources in optimizing quantum thermal machines.

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arXiv2024

Quantum synchronization between two spin chains using pseudo-bosonic equivalence

Quantum synchronization among many spins is an intriguing domain of research. In this paper, we explore the quantum synchronization of two finite chains of spin-1/2 particles, via a nonlinear interaction mediated by a a central intermediary spin chain. We introduce a novel approach using the Holstein-Primakoff transformation to treat the spin chains as pseudo-bosonic systems and thereby applying the synchronization criteria for harmonic oscillators. Our theoretical framework and numerical simulations reveal that under optimal conditions, the spin chains can achieve both classical and perfect quantum synchronization. We show that quantum synchronization is robust against variations in the number of spins and inter-spin coupling, though may be affected by thermal noise. This work advances the understanding of synchronization in multi-spin systems and introduces a generalized synchronization measure for both bosons and fermions.

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arXiv2024

Quasi-probability distribution of work in a measurement-based quantum Otto engine

We study the work statistics of a measurement-based quantum Otto engine, where quantum non-selective measurements are used to fuel the engine, in a coupled spin working system (WS). The WS exhibits quantum coherence in the energy eigenbasis at the beginning of a unitary work extraction stage in presence of inter-spin anisotropic interaction. We demonstrate that the probability of certain values of stochastic work can be negative, rendering itself akin to the quasi-probability distribution found in phase space. This can be attributed to the interference terms facilitated by quantum coherence. Additionally, we establish that coherence can improve the average work in finite time. Subsequently, we compare the work distribution with a standard QOE operating between two heat baths. We find that, because of the absence of quantum coherence, the probability of stochastic work cannot be negative in a standard QOE.

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arXiv2023

Anisotropy-assisted thermodynamic advantage of a local-spin thermal machine

We study quantum Otto thermal machines with a two-spin working system coupled by anisotropic interaction. Depending on the choice of different parameters, the quantum Otto cycle can function as different thermal machines, including a heat engine, refrigerator, accelerator and heater. We aim to investigate how the anisotropy plays a fundamental role in the performance of the quantum Otto engine operating in different time scales. We find that while the efficiency of the engine efficiency increases with the increase in anisotropy for the quasistatic operation, quantum internal friction and incomplete thermalization degrade the performance in a finite time cycle. Further, we study the QOE with one of the spins, the local spin, as the working system. We show that the efficiency of such an engine can surpass the standard quantum Otto limit, along with maximum power, thanks to the anisotropy. This can be attributed to quantum interference effects. We demonstrate that the enhanced performance of a local-spin QOE originates from the same interference effects, as in a measurement-based QOE for their finite time operation.

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arXiv2023

Quantum synchronization and entanglement of indirectly coupled mechanical oscillators in cavity optomechanics: a numerical study

It is often conjectured that quantum synchronisation and entanglement are two independent properties which two coupled quantum systems may not exhibit at the same time. However, as both these properties can be understood in terms of the second order moments of a set of conjugate quadratures, there may exist specific conditions for simultaneous existence of entanglement and quantum synchronization. Here we present a theoretical scheme to achieve the same between two mechanical oscillators, which are indirectly coupled with each other via a coupling between two cavities. We show that in the presence of the cavity-oscillator coupling, quadratically varying with their displacements, these oscillators can be synchronized in the quantum sense and entangled as well, at times much longer than the decay time-scale of the cavity modes. Precisely speaking, we show that in the presence of quadratic coupling, entanglement criterion and quantum synchronization measure are simultaneously satisfied in steady state. This behaviour can be observed for a range of quadratic coupling, temperature, and frequency difference of the two oscillators.

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arXiv2023

Entanglement as a sufficient condition for quantum synchronization between two mechanical oscillators

We present an optomechanical model to show that entanglement can be a sufficient condition for quantum synchronization of two mechanical oscillators. As both these entities can be characterized in terms of variances of a set of EPR-like conjugate quadratures, we investigate whether this leads to a specific condition for simultaneous existence of the both. In our model, one of the oscillators makes the cavity, while the other is kept suspended inside the cavity, and the always-on coupling between the two is mediated via the same cavity mode. We show that in presence of amplitude modulation with the same frequency as that of the oscillators, these oscillators get nearly complete quantum synchronized and entangled simultaneously in the steady state. We also show that entanglement always becomes accompanied by quantum synchronization, though the reverse is not necessarily true. Thus, entanglement becomes a sufficient condition for the quantum synchronization. This behaviour can be observed for a large range of system parameters.

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arXiv2023

Measurement-based quantum Otto engine with a two-spin system coupled by anisotropic interaction: enhanced efficiency at finite times

We have studied the performance of a measurement-based quantum Otto engine (QOE) in a working system of two spins coupled by Heisenberg anisotropic interaction. A non-selective quantum measurement fuels the engine. We have calculated thermodynamic quantities of the cycle in terms of the transition probabilities between the instantaneous energy eigenstates, and also between the instantaneous energy eigenstates and the basis states of the measurement, when the unitary stages of the cycle operate for a finite time $τ$. The efficiency attains a large value in the limit of $τ\rightarrow 0$ and then gradually reaches the adiabatic value in a long time limit $τ\rightarrow \infty$. For finite values of $τ$ and for anisotropic interaction, an oscillatory behaviour of the efficiency of the engine is observed. This oscillation can be interpreted in terms of interference between the relevant transition amplitudes in the unitary stages of the engine cycle. Therefore, for a suitable choice of timing of the unitary processes in the short time regime, the engine can have a higher work output and less heat absorption, such that it works more efficiently than a quasi-static engine. In the case of an always-on heat bath, in a very short time the bath has a negligible effect on its performance.

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arXiv2022

Strong entanglement criteria for mixed states, based on uncertainty relations

We propose an entanglement criterion, specially designed for mixed states, based on uncertainty relation and the Wigner-Yanase skew information. The variances in this uncertainty relation does not involve any classical mixing uncertainty, and thus turns out to be purely of quantum mechanical nature. We show that any mixed entangled state can be characterized by our criterion. We demonstrate its utility for several generalized mixed entangled state including Werner states and it turns out to be stronger than any other known criterion in identifying the correct domain of relevant parameters for entanglement. The proposed criterion reduces to the Schrodinger-Robertson inequality for pure states.

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arXiv2021

Finite-time performance of a single-ion quantum Otto engine

We study how a quantum heat engine based on a single trapped ion performs in finite time. The always-on thermal environment acts like the hot bath, while the motional degree of freedom of the ion plays the role of the effective cold bath. The hot isochoric stroke is implemented via the interaction of the ion with its hot environment, while a projective measurement of the internal state of the ion is performed as an equivalent to the cold isochoric stroke. The expansion and compression strokes are implemented via suitable change in applied magnetic field. We study in detail how the finite duration of each stroke affects the engine performance. We show that partial thermalization can in fact enhance the efficiency of the engine, due to the residual coherence, whereas faster expansion and compression strokes increase the inner friction and therefore reduce the efficiency.

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arXiv2018

Critical-point behavior of a measurement-based quantum heat engine

We study how a quantum heat engine performs across the critical value of an external parameter, pertaining to the quantum phase transition. Considering a two-ion system subjected to a magnetic field, we show that the system performs in a quantum Otto cycle above a critical value of the magnetic field, while below such critical point, it does not operate in a heat cycle at all. Moreover, at the critical point, its interaction with an ancillary ion deteriorates the performance of the system as a heat engine. We further show that a strong interaction between the constituent ions of an ion-based system is crucial for it to work in a heat-work cycle, while the coupling to the ancillary system must be minimized.

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arXiv2017

Adiabatic transfer of energy fluctuations between membranes inside an optical cavity

A scheme is presented for the adiabatic transfer of average fluctuation in the phonon number between two membranes in an optical cavity. We show that by driving the cavity modes with external time-delayed pulses, one can obtain an effect analogous to stimulated Raman adiabatic passage (STIRAP) in the atomic systems. In this adiabatic processes the population is trapped between two states by creating a dark state.The adiabatic transfer of fluctuation from one membrane to the other is attained through a 'dark' mode, that is robust against decay of the mediating cavity mode.The results are supported with analytical and numerical calculations with experimentally feasible parameters.

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arXiv2017

Single-ion quantum Otto engine with always-on bath interaction

We demonstrate how a quantum Otto engine (QOE) can be implemented using a single ion and an always-on thermal environment. The internal degree of freedom of the ion is chosen as the working fluid, while the motional degree of freedom can be used as the cold bath. We show, that by adiabatically changing the local magnetic field, the work efficiency can be asymptotically made unity. We propose a projective measurement of the internal state of the ion that mimics the release of heat into the cold bath during the engine cycle. In our proposal, the coupling to the hot and the cold baths need not be switched off and on in an alternative fashion during the engine cycle, unlike other existing proposals of QOE. This renders the proposal experimentally feasible using the available tapped-ion engineering technology.

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arXiv2017

Measurement-induced operation of two-ion quantum heat machines

We show how one can implement a quantum heat machine by using two interacting trapped ions, in presence of a thermal bath. The electronic states of the ions act like a working substance, while the vibrational mode is modelled as the cold bath. The heat exchange with the cold bath is mimicked by the projective measurement of the electronic states. We show how such measurement in a suitable basis can lead to either a quantum heat engine or a refrigerator, that undergoes a quantum Otto cycle. The local magnetic field is adiabatically changed during the heat cycle. The performance of the heat machine depends upon the interaction strength between the ions, the magnetic fields, and the measurement cost. In our model, the coupling to the hot and the cold baths are never switched off in an alternative fashion during the heat cycle, unlike other existing proposals of quantum heat engines. This makes our proposal experimentally realizable using current tapped-ion technology.

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arXiv2017

Motion-induced enhancement of Rabi coupling between atomic ensembles in cavity optomechanics

We propose a scheme of enhancement of Rabi coupling between two identical atomic ensembles trapped inside an optical cavity in a membrane-in-the-middle set up. The cavity modes dispersively interact with the ensembles and the effective interaction between the ensembles is governed by the tunnelling rate of the cavity modes through the oscillating membrane. We have shown that this interaction can be made large enough such that the Rabi oscillation occurs in a time-scale, much smaller than the relevant decay time-scales of the cavity modes and of the membrane. We present the detailed analytical and numerical results and assess the feasibility of the scheme using currently available technology.

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arXiv2016

Two-atom quantum gate in hybrid cavity optomechanics

Tracing the dynamics of a quantum system using a mesoscopic device is an important topic of interest nowadays. Here we show how a mesoscopic mechanical oscillator steers the dynamics of a coupled two-atom system and gives rise to a two-qubit SWAP gate. We have theoretically studied a generic hybrid atom-optomechanical system where two identical atoms in $Λ$ configuration are trapped inside the cavity and the cavity mode mediates the interaction between the atoms and the mechanical oscillator. Adiabatic elimination of the lossy channels is adopted which in turn gives rise to an effective Hamiltonian that is responsible for a two-atom SWAP gate controlled by the mechanical motion of the oscillator. The validity of the proposal for successful implementation is assessed using presently available experimental parameters.

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